Romney would have no authority to “repeal” anything on day one. ONLY Congress has the authority to repeal anything. What Mitt said was that he would offer waivers to any state which wanted one. That has not changed. That is an effective repeal.
The Court decision has actually made it easier to repeal Obamacare by declaring it a “tax”. This means it can be part of a “reconciliation” bill and therefore not subject to filibuster.
Most of it will be repealed. There may be some things in its 2000 pages which are not bad ideas. Ryan would know.
In fact he did say that, but I know he can't do that, at least not constitutionally, but what the heck, Congress doesn’t seem to mind anymore.